An emulsion is a dispersion of one liquid in another liquid and generally is in the form of a water-in-oil mixture having an aqueous or water phase dispersed within a substantially immiscible continuous oil phase. Water-in-oil (or oil in water) emulsions having a high ratio of dispersed phase to continuous phase are known in the art as High Internal Phase Emulsions, also referred to as “HIPE” or HIPEs. At relatively high dispersed aqueous phase to continuous oil phase ratios the continuous oil phase becomes essentially a thin film separating and coating the droplet-like structures of the internal, dispersed aqueous phase. In certain HIPEs continuous oil phase comprises one or more polymerizable monomers. These monomers can be polymerized, forming a cellular structure, for example a foam, having a cell size distribution defined by the size distribution of the dispersed, aqueous phase droplets.
HIPE foams can be formed in a continuous process, wherein a HIPE is formed and then moved through the various stages used to produce a HIPE foam. A movable support member, such as a belt, will typically be used to move a HIPE from one stage to the next. Following the formation of the HIPE the next stage involves the polymerization of the monomers present in the oil phase to produce a HIPE foam. Initiator, which is used to start polymerization, is generally added during HIPE formation either to the separate aqueous and continuous oil phases or to the HIPE during the emulsion making process. In addition to the presence of initiator heat can be used to accelerate the polymerization reaction, for example the individual aqueous and oil phases may be heated to accelerate the polymerization reaction.
The environmental conditions used to polymerize a HIPE into a HIPE foam can be very harmful to equipment, such as belts. For instance polymerization of a HIPE often involves the use of high temperatures. Further, to minimize fluid loss in HIPEs during the polymerization process and to provide a more equalized temperature distribution, steam may be used as the heat source. The steam can penetrate the materials in the belt and cause the belt to swell. Further, HIPEs are often produced using one or more types of corrosive salts, which can migrate, enter the belt and degrade it. In addition to the use of heat to polymerize HIPEs other methods can be used that are harmful to belts, such as the use of actinic radiation supplied by an ultraviolet source.
These harsh environments while beneficial to the polymerization of HIPEs can be harmful to the belts upon which HIPEs are extruded and transported on. These environments are not only directly harmful to the belts and facilitate their deterioration; they can also affect the quality of the HIPE foam produced from such belts. HIPEs in a continuous process are often extruded onto the surface of a belt as a thin sheet. If the belt has imperfections on its surface these imperfections can negatively influence the HIPE extruded thereon. For example, if the belt has bulges or bumps on its surface these imperfections can result in uneven HIPE foam sheets, or sheets having holes, which cannot be used. Further if the HIPE foam requires an open celled structure on its surface, for the absorption of liquids, a damaged belt surface could cause the HIPE foam surface to have a closed cell structure, and therefore inhibit the intended function of the HIPE foam. Additionally, at some point in the HIPE foam process, the HIPE foam will need to be detached from the belt, and if the belt surface is uneven or damaged the HIPE foam might be damaged during the removal step as the HIPE foam will adhere to the belt surface.
One potential solution to providing a suitable belt surface has been to use various methods to strengthen or enhance a belt surface, for example, by laminating or impregnating a belt surface with materials that will provide a smooth belt surface, such as Teflon or resins. These materials have a number of technical drawbacks, such as successfully adhering the materials to a belt surface, and while potentially lengthening the life of a belt are very costly, and will eventually fail. Another method has involved the use of a film layer which resides on and moves along with the surface of a belt and unto which a HIPE is extruded. However, there also have been drawbacks to this approach. A HIPE is transported in a continuous process through the use of endless belts, which at their ends have pulleys. The pulleys stretch the outer surface of a belt, but once the belt passes the pulley the belt contracts back to its original shape. These changes in the outer surface of the belt cause the film residing on the belt surface to fold back upon itself forming ripple across the film surface, as the belt contracts. The ripples produced cause deformations in the HIPE extruded on them.
A further problem of using belts in the HIPE foam making process relates to the static nature of the belts used to transport the HIPEs through the HIPE foam making process, and therefore also any films resting on the belts. When starting the process by extruding a HIPE onto a belt surface, the HIPE that is first extruded is often not usable to produce a HIPE foam. One attempted solution has been to try and make the extruding devices mobile. This has proved problematic for several reasons, the first of which relates to the size of the extruding device required, in that to produce HIPE foams at a high rate a relatively large extruding device is needed to extrude large quantities of HIPE onto a belt, such size makes the extruding devices bulky and difficult to move. Another factor is the quality of the HIPE extruded onto the belt, in that movement of the extruding device could cause the HIPE being extruded to be extruded unevenly—leading to non-usable HIPE foam. A further consideration is the extruding devices are substantially fixed in place by the HIPE feed lines that supply them. Another attempt to solve the problem has been to try and make the belt that the HIPE is extruded on mobile. This has not proven usable as moving the belt slackens the tension in the belt leading to HIPE that is once again unevenly extruded; and as with the extruding device, causing extra movement of the belt creates an unstable surface for the HIPE, once again resulting in uneven extrusion of the HIPE. Further, long belts require high tension in order to be driven to overcome drag forces, and wider systems provide economies of scale, hence the support structures and the pulleys themselves have to be substantial, making the movement of said structures more difficult, especially more difficult to do accurately time after time.
Therefore there exists a need for a way to protect a belt surface for HIPE foam formation in a continuous process, and while doing so also provide a system that allows for the selection of which HIPE is used to produce HIPE foam.